Essentially this is 2/3 of the brutal Ilya Muromets build. Two UACs and two medium lasers. To go AC/20, just swap out the engine and ballistics.
My concern with this build is the weight of the autocanons. You need an XL (=> quick death) for an only decent engine, or you're painfully slow with a standard. I tested a similar build few months ago and quickly went back to an AC/20 build. (to be totally honest, it also had to do with the fact that I suck at not jamming the UAC)
I picked up the UAC5s to run more-or-less this exact setup. It's decent on paper (I run an XL in my AC20 loadout too) but the UAC5s are focused with time-on-target shooting instead of the hit-and-run I find myself always doing to stay alive in my Wang.
Yeah, I found even with a lot of time on target, the AC/20 is better. There's just something about pinpoint damage that is more important than DPS in this game. Still, this option is available for those who want to do something different, and as I mentioned in the OP, all you need to do is swap out the engine and ballistics. If you do what I do and just pop engines in and out, you're bound to have a 255 XL sitting around.
I gave this mech another try. I use a slightly different loadout, with one less ton of ammo and 1/2 less ton of armor, but a bigger engine: It's nice to be able to engage at longer range (that's my main reason for leaving the AC/20). It's mobile, has a good DPS. But, it's fragile: it's rare I run out of ammo, most of the time my arm is destroyed before. The arm is destroyed really quickly, quick like AC/40 quick: Just like YYY said, the build is better on paper than on the field.
I quite like this build. You need to have the ability to snapshot then move, even though you have a Ultra-AC. Wait until you get a distracted opponent before unleashing the "ultra". Anything else and you're just too squishing to stand toe to toe. I did, however, adjust the ammo loadout and armor allocation a bit.
This Build and the BFG Build are the only true Reasons to run the YLW. The other ones rather for J4F. As some mentioned before, the D can do everything too, except for the mentioned two builds. IMO this build here is more useful than the BFG Build, although it is theoretically safer to run a STD Engine, but what does it help you, if in Close Range Brawls your Cannon Arm gets blasted off too quickly? Run it against Pro Gamers and you know what i mean. This here with 5-6 Tons Ultra AC Shells is imho the most effective build for the YLW. 5-6 Stars definitely. If you die by ST.Explosion your own fault letting this happen. As a Secondline Firesupporter this build shines like a rising sun. No Question. Keep distance and empty your clips before going Kamikaze Mode! Here is my Ultra Ammo Version:
I broke smurfy's! While this might look like a sexy upgrade, this build has 2 slots too much, luckily didn't try to build it yet and hopefully I warn people in time ^^: